Cracking and damage behavior of tungsten under ELM's like energy loads using millisecond laser pulses

In this work, ELM-like conditions were replicated by exposing tungsten surface to the repetitive millisecond laser pulses, and the damage and surface modification were studied. At a pulse duration of 3 ms, the damage and cracking threshold was found at 0.2-0.3 MJ m−2 while the melting was observed after 0.5 MJ m−2 which shifted to lower energy load with increasing the number of shots. In addition, these thresholds significantly dropped to lower energy densities with reduction in pulse durations. At same energy load (0.42 MJ m−2), solid particles were ejected from irradiated surface exposed to 3 ms pulses while both solid and liquid droplets splashed from melt layer were observed from surface irradiated with 1 ms pulses. Analysis of exposed W surface and particles ejection from the treated surface indicate that there is no qualitative differences between ion beam and long pulse lasers to simulate the ELM like transient conditions at laboratories.